two things that could be wrong (hard to say with the info you are giving)

a) Create at pure domain an A record with as host @ and point it to your server.

or

b) In ISPconfig go to ISPmanager, and select the domain (somesite.com)
Now go to the Co-domains tab, and click on NEW. Leave the "Hostname:" empty, and enter in the "Domain:" somesite.com
When done, click on save.